1. Field of the Invention
This invention relates to a method for heat-sterilizing a blood powder (e.g., plasma powder, serum powder, corpuscle powder, whole blood powder) obtained from the blood of livestock, for example, killed in slaughter-houses, in order to obtain a rheological binding agent suitable for an increase of the quality of the processed foodstuff using the blood powder.
2. Description of the Prior Art
Attempts have been made heretofore in various countries to produce blood powders from the blood of slaughtered animals and to use the powders as foodstuffs or feeds, for example. Blood powders for feeds are being produced also in some slaughter-houses in Japan. Blood powders have also been suggested for foodstuff. In recent years, there has been a worldwide need for securing sources of animal proteins. Since blood proteins are nutritionally complete proteins and have superior properties such as water solubility and heat coagulability, there has been an increasing demand for the utilization of blood powders for foodstuff. Sterilizing techniques, however, have posed a problem in utilizing blood powders in foodstuffs.
The conventional sterilizing method comprises feeding steam directly into the collected blood. However, this method causes a denaturation of the proteins, a loss of the water solubility and a loss of the heat coagulability of the blood powder which are required as foodstuffs. Hence, the usefulness of the blood powder in foodstuffs is very much reduced. Methods which have been suggested or are being performed for production of edible blood powders involve whole blood or separating the collected blood into plasma or serum and corpuscles, and drying the fractions, e.g., by spray-drying, lyophilizing or vacuum drying, separately to produce blood powders without denaturing the proteins. However, since the temperature used for concentration and drying is low, the blood powders cannot be sterilized at the temperature used. No effective technique for sterilizing such blood powders has been developed.
For example, in the case of drying foodstuffs by a spray-drying, generally, the drying is carried out using an air flow of about 150.degree. to 180.degree. C. but the moisture is momentarily evaporated, and as a result, the temperature of the dried product is maintained at a low temperature of about 50.degree. to 60.degree. C. or less by the latent heat of evaporation and never increases, and in the case of drying foodstuffs by a vacuum drying, since the boiling point is determined depending upon the vacuum degree, it is possible to limit the heating temperature of the dried product to 60.degree. C. or less in accordance with the vacuum degree. Thus, in the above drying processes, the blood powder can be dried at 60.degree. C. or less. However, since the temperature of the substance heated is low, a sterilizing effect cannot be obtained at all.
Water solubility and heat coagulability are among the properties of blood powder which are required for use in foods. In general proteins, these properties are easily lost by heating. Alternatively, sterilizing methods using chemicals or by filtration are conceivable. However, these alternative methods are difficult to put into practice because of the adverse effects on the human body or because of the high production cost. No effective method for sterilizing blood powders without denaturing the proteins has been developed heretofore.